In a gas burner, it is necessary to secure a most appropriate proportion between a raw gas flow rate and an air flow rate in order to obtain a complete combustion.
To this end, heretofore, a primary air and a secondary air which were to be fed to a gas burner were controlled by properly varying the number of rotation of a centrifual blower or reducing the aperture of an air intake port of an air blower by means of an electronic control circuit or the like, and the raw gas which was to be fed to the gas burner was regulated in flow rate by increasing or decreasing the degree of the opening degree of a gas delivery valve.
However, according to such control means as mentioned, although there was no problem when the gas burner was at high load combustion, if a pressure change (an external factor, a rush of wind, etc.) should occur at the exhaust port side of the gas burner when the gas burner was at low load combustion, it had the shortcomings in that the flame of the gas burner was blown out, that carbon monoxide was generated, or that a back phenomenon of a flame was taken place and as a result, that a proper combustion was difficult to obtain.
Furthermore, the conventional control method had the shortcoming in that since the ratio of a secondary air with respect to a primary air was impossible to control, the generation of a combustion noise was difficult to restrain.
It is therefore an object of the present invention to provide a gas-air ratio control valve for gas burners, in which such shortcomings as inherent in the prior art as mentioned can be overcome, the flame of a gas burner is not blown out even if a pressure change (an external factor, a rush of wind etc.) is taken at an exhaust port side of the gas burner, a carbon monoxide is not generated, the back phenomenon of a flame can be prevented from being taken place, and as a result, a proper combustion can be obtained.